1. Field of the Invention
The present invention relates to a surface defect inspection apparatus for inspecting a defect on a track of a recording medium having a plurality of tracks or of a stamper thereof or the like.
2. Description of Related Art
In a process for manufacturing an optical disc, for example, if any dust is stuck to a surface of a stamper thereof and such a defect 31 on a stamper 21 is formed as shown to be enlarged in FIG. 1, there forms a dented defect 32 of the same configuration at the same position as that of the stamper 21 on a surface of an optical disc 22 made by using the stamper 21 as shown to be enlarged in FIG. 2.
A lot of defects such as 31 and 32, or those of various configurations and sizes, can be formed on the whole surface of the stamper or of the optical disc. However, those defects 31 and 32 are so minute that it is essentially impossible to find them only by visually inspecting the surface of the stamper 21 or of the optical disc 22. In order to inspect those defects, there has been used such a surface defect inspection apparatus as shown in FIG. 3 or FIG. 4. In FIG. 3, an object 1 to be inspected such as the optical disc or the stamper thereof is rotated by a motor 2. Above the object 1 is provided an optical head 11 having a light-emitting and light-receiving surface faced to the surface of the object 1, its output being inputted to a defect position detector 12. A rotating signal of the motor 2 is also inputted to the detector 12, the detector 12 giving the motor 2 a driving signal. Output of the detector 12 is inputted to an indicator 13 such as a printer or a plotter.
If any defect on the track of the object 1 is inspected by this surface defect inspection apparatus, the motor 2 is driven in response to the driving signal from the detector 12 so that the object 1 is rotated. In addition, if the object 1 is moved from the outer periphery to the inner periphery thereof, for example, while light is emitted from the optical head 11 thereto, the optical head 11 detects the reflected light on each track of the object 1 one by one and a signal related to the reflected light is obtained. In other words, a signal related to the configuration of the track of the optical disc is inputted to the detector 12. The detector 12, in connection with the rotation of the motor 2, receives a position signal for specifying the position of the radial direction of the object 1 and the circumferential direction of the track, which is made to be in correspondence to the detecting signal of the optical head 11 so as to be inputted to the indicator 13. The indicator 13, thereby, indicates the condition of the defect on the track of the object 1.
In FIG. 4, the object 1, which is adapted to be rotated by the motor 2, can linearly be moved in the radial direction thereof together with the motor 2 by a straight line driver 3. There is provided closely above the object 1 an automatic focusing microscope 6 having the wide visual field toward the surface of the object 1, its light emitting side being linked to an optical path transfer 14. A television camera 8 is linked to one light emitting side 14a of the optical path transfer 14 and carmeral 7 is linked to the other light emitting side 14b thereof. Output signal from the television camera 8 is sent to a monitor 9 and a printer 10, respectively.
If any defect on the track of the object 1 is inspected by this surface defect inspection apparatus, the object 1 is rotated by the motor 2 as well as moved in the radial direction thereof together with the motor 2 by the straight line driver 3. The microscope 6 is focused on the track of the object 1 by automatic focusing thereof. Each track of the object 1 is moved one by one in the visual field of the microscope 6, thereby, the condition of each track of the object 1 is observed. The image of the observed condition of the track is picked up by the television camera 8, whose output signal is sent to the monitor 9 so as to be indicated therein or to the printer 10 so as to be printed. In addition to the above process, by transferring the optical path transfer 14, the image in the visual field of the microscope 6 can be picked up by the camera 7.
In one conventional apparatus as shown in FIG. 3, a signal corresponding to the defect of the track is obtained from the optical head 11 so that the length of the defect being formed can be detected. There are so few plane defect surfaces that the reflected light from the defect surface can be dispersed, as a result, a signal outputted from the optical head 11 has little variation in the periphery of the defect. Therefore, the apparatus has a disadvantage that the size and configuration of the defect can not be inspected.
In the other conventional apparatus as shown in FIG. 4, since the microscope 6 observes the condition of the track, the size and configuration of the defect can be inspected. However, regardless of whether there is a defect or not, since the whole track of the object 1 is observed by the microscope 6, if the object 1 has few defects, there exists a disadvantage that effective inspection of defects can not be performed, spending useless time for it.